In a conventional single-sheet printer, paper is directed through a print cycle which includes picking up a sheet of paper, feeding it into the printer, and then expelling it through the printer's output port. Once expelled, the sheet falls to an output tray, consecutive sheets thus piling one on top of the other to form an output stack. Ideally, the sheets will fall directly to the tray, forming a stack made up of substantially vertically aligned sheets. Such a stack is desirable in both personal and business applications, offering a stack which is substantially stable and easily manipulable for later sheet processing.
Sheets expelled by conventional printers, however, rarely fall directly to the output tray. Instead, sheet fall is made random by a variety of aerodynamic forces, such forces producing an effect known generally in the industry as "sail". Sheet sail most often is characterized by the sheet cutting through the air so as to glide in the direction of sheet expulsion, potentially passing beyond the confines of the output tray. Such an effect results in an increasingly destabilized stack, often culminating in sheets spilling onto the floor and requiring hand restacking of the sheets.